CTB-004 Color Temperature Blue (Cooling) Filter
3/4 CTB colour-conversion filter shifting 3200 K toward 4800 K for seamless mixed-lighting balance in broadcast, film, and architectural applications.
- Colour shift direction: Cooling (3200 K → 4800 K)
- Mired shift: −100 Mired
- Correction strength: 3/4 CTB
- Average transmittance: ~48.6 % T (visible range)
- Peak transmittance: ~93.7 % T near 439 nm
- Minimum transmittance: ~20.6 % T near 701 nm
- Construction: Ion-assisted hard-oxide; 5 – 450 mm shapes, 0.21 – 3.8 mm thick
- Custom options: Intermediate Mired shifts, combined CTB+diffusion, custom sizes, rapid prototypes
Learn more
CTB-004 CTB delivers Colour shift direction Cooling (3200 K → 4800 K), Mired shift −100 Mired, and Correction strength 3/4 CTB.
The hard-oxide coating is built for repeated handling, heat, and cleaning.
Best suited for:
Three-quarter CTB correction provides a strong cooling shift that brings tungsten sources close to daylight without complete conversion — suited for controlled partial correction
Description
CTB-004 gives tungsten or warm-white LED sources a noticeable cool-up—roughly a ½-CTB step—without wiping out output the way a full CTB film would. Transmittance rises through three distinct peaks— 85 % at 388 nm, ~94 % at 440 nm, and ~93 % at 492 nm. Transmittance never drops below 70 % from the near-UV edge at 380 nm right through to about 513 nm, delivering consistent, high-output energy across the entire violet-to-blue-green band before the curve begins its controlled roll-off. Beyond 515 nm it slopes away, dropping to ~50 % by 525 nm, ~33 % around 550 nm, reaching a low of ~20 % at 700 nm, and edging back up toward ~34 % by 780 nm. The smooth taper prunes red/amber energy enough to lift a 3200 K lamp toward 4300 – 4500 K while preserving plenty of green so skin tones stay natural.
Key advantages
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Mid-strength ½-CTB correction – Raises CCT by roughly 1500–1800 K, ideal for balancing tungsten with cool LED backlights or mild daylight spill.
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High blue-region throughput – ≥ 80 % between 440 – 500 nm keeps fixtures punchy compared with deep-blue gels.
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Progressive red attenuation – Smooth roll-off avoids cyan shifts or green spikes that complicate colour grading.
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Heat-robust oxide stack – All-glass coating survives 1 kW halogen, high-power LED engines, and frequent cleaning.
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Custom formats – Round, square, or free-form parts from 5 mm to 450 mm, 0.21 – 3.8 mm thick, on Borofloat®, soda-lime, Schott D263 T, or Corning Eagle XG glass.
Typical applications
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Stage & architectural lighting – Cool house tungsten rigs to blend with video walls or daylight apertures.
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Film & broadcast – Ease practical lamps a half-step toward daylight so they grade cleanly with HMIs and skylight.
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Photography modifiers – Add a subtle blue lift without stacking multiple gels that cut output.
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Museum & retail displays – Improve colour rendition and whiteness without introducing damaging UV.
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Machine-vision & inspection – Enhance blue-channel contrast for fluorescent brighteners or security inks while maintaining overall brightness.
Need a prototype within days or a production run next month? CTB-004 filters can be coated, cut, and shipped to your exact specification—fast.
FAQ
CTB-004 FAQ
What is CTB-004 and what is it used for?
CTB-004 is a Strong Blue Shift with Extreme UV Extension. CTB-004 combines aggressive blue enhancement with exceptional UV transmission, peaking at 93.7 % at 439nm while reaching 79 % UV passage. With a 50 % transmission point at 528nm, this strong CTB filter delivers decisive tungsten-to-daylight conversion while maintaining near-complete UV propagation. Common uses include Fluorescence Microscopy, Scientific Photography, Extreme Tungsten Conversion, and Multi-spectral Imaging.
What are the key optical specs of CTB-004?
Key published specs for CTB-004 include Colour shift direction: Cooling (3200 K → 4800 K); Mired shift: −100 Mired; Correction strength: 3/4 CTB; Average transmittance: ~48.6 % T (visible range); Peak transmittance: ~93.7 % T near 439 nm.
What applications is CTB-004 best suited for?
CTB-004 is commonly used for Fluorescence Microscopy, Scientific Photography, Extreme Tungsten Conversion, and Multi-spectral Imaging. Fluorescence Microscopy - Shift tungsten illumination toward daylight while preserving UV excitation energy for fluorescent probe imaging and cellular analysis.
Can CTB-004 be customized for size, substrate, or coating requirements?
KUPO lists the construction for CTB-004 as Ion-assisted hard-oxide; 5 – 450 mm shapes, 0.21 – 3.8 mm thick. Published custom options include Intermediate Mired shifts, combined CTB+diffusion, custom sizes, rapid prototypes. Standard and Custom Formats - Round (5-450mm), square, and free-form geometries on Borofloat, soda-lime, Schott D263 T, or Corning Eagle XG substrates; 0.21-3.8mm thickness range.
What should I know about angle of incidence and durability for CTB-004?
The hard-oxide coating is built for repeated handling, heat, and cleaning.
